Pigment spacing

ABSTRACT

An improved pigment spacing composition and method of manufacture. A coating composition wherein the pigment particles are spaced more uniformly resulting in improved coating properties. In another embodiment, the present invention relates to a composition having nanoparticles interacting with pigmentary titanium dioxide to provide for more uniform spacing of the titanium dioxide.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/914,594 filed on Aug. 9, 2004 which is incorporated herein byreference

FIELD OF THE INVENTION

The present invention is generally related to controlling pigmentspacing in a coating composition. More particularly, the presentinvention is related to achieving an improved TiO₂ spacing in a paint,such as by using nanoparticles of ZnO, SiO₂, or Al₂O₃ of differing sizeand density distribution.

BACKGROUND OF THE INVENTION

Pigments such as titanium dioxide are a common component of coatingcompositions, particularly paint. Paint generally comprises afilm-forming material or binder, a pigment, and a carrier or solventwhich evaporates to leave the solids as a coating on a substrate.

The pigment is generally partially or wholly suspended or dissolved inthe carrier. Film formation of paint occurs when the paint is applied toa substrate and the carrier evaporates. During this process, theparticles of pigment and binder come closer together. As the lastvestiges of liquid evaporate, capillary action draws the binderparticles together with great force, causing them to fuse and bind thepigment into a continuous film. This process is often referred to ascoalescence.

Thus, the spacing and orientation in the carrier of the pigmentparticles relative to each other, and the various other solids, isessentially retained when the solid film is formed on the substrate.Flocculation and settling of the pigment phase are particularlyundesirable. The pigments tend to cling together as packed pigmentparticles by agglomerating or clustering and then tend to resistsubsequent redispersion by agitation, thus degrading the hiding power ofthe resulting paint. Hiding power is among one of the most importantattributes of paint, and hiding power is determined particularly inwhite paint by the light scattering effectiveness of the pigment. Thelight scattering effectiveness of the pigment is in turn highlydependent on the spacing arrangement of the pigment in the dried coatingas well as the particle sizes. Many different methods are known in theart for affecting and controlling the sizes of the pigment particles;however, this has proven to be ineffective in controlling lightscattering sufficiently.

The pigment which is most widely used in paint is titanium dioxide.However, titanium dioxide is relatively expensive in comparison to thecosts of other components used in paint. As such, there is a need tomaximize the beneficial aspects of titanium dioxide, while minimizingthe amount used. Enhanced light scattering occurs when the titaniumdioxide pigment particles have a diameter of about 200 to 300 nm and areuniformly spaced about the same distance apart. Most commonly,particulate TiO₂ in the range of 100 nm to 400 nm is utilized inconventional paint.

Various techniques have been attempted and used in the art to promote aneven spacing and distribution of the pigment in the coating. A number ofpigments have been found to function as “extender” pigments, wherein theextended pigments are alleged to function in mechanically spacing theopacifying or “prime” pigments. However, the flocculation forces presentduring the drying of paint still result in the presence of clusters andflocs of pigment particles. Thus, even if total deaggregation isaccomplished in the dispersion process, a random distribution of pigmentparticles will not approach the theoretical optimum that an ideallyspaced distribution would achieve.

Regardless of the technique, prior art coatings do not achieve a levelof opacity which approaches that predicted theoretically. Thus, there isa long felt need for further improvement, such as a more efficientpacking arrangement of TiO₂ particles in a coating formed on asubstrate.

SUMMARY OF THE INVENTION

The present invention provides methods and compositions for coatingswherein the TiO₂ particles exhibit improved spacing over conventionalpaint formulations. Without limiting the scope of the invention, it isbelieved that the nanoparticle-sized pigment particles (specificallynano-ZnO) have an affinity for the surface of pigmentary TiO₂ particles.It is therefore believed that the nano ZnO particles effectively aredisposed around and associated with the TiO₂ particle so that theefficiency of the TiO₂ particles arrangement increases; i.e., theoverall stability of TiO₂ pigment particles on drying is improved, thusimproving properties such as tint strength and hiding power (contrastratio). It is believed that the nano ZnO particles are interacting withthe TiO₂ to form a more efficient dispersion.

In one embodiment, a method is provided for producing a titanium dioxideparticle dispersion having nano-particle pigments interacting with thetitanium dioxide to provide for more efficient packing arrangement ofthe titanium dioxide. In a preferred embodiment, the present inventionrelates to a paint composition of titanium dioxide, and a nanoparticlepigment, such as ZnO, and also a binder and a dispersant, along withadditives as known in the art for formulating paint. The nanoscale zincoxide, silicone dioxide, and aluminum oxide provide for a more uniformdispersment of the titanium dioxide when the paint dries to form acoating on a substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents the ideal spacing of TiO₂ particles;

FIG. 2 is a representation of how TiO₂ particles are spaced in a typicalprior art paint; and

FIG. 3 is a representation of one embodiment of the present inventionshowing nano ZnO particles in association with TiO₂ particles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is known that efficient spacing of TiO₂ particles in a paint producesa paint that has improved tint strength and hiding power. However, inmost paints, upon drying, the TiO₂ pigment particles agglomerate andthus reduce the efficiency of the TiO₂ particles. This agglomeration ofTiO₂ particles yields paints that have lower tint strength and hidingpower.

It is believed in accordance with the principles of the presentinvention that the nanoparticle-sized pigment particles (specificallynano-ZnO) are uniformly distributed within the paint matrix. Throughthis uniform distribution of particles, higher tint strength and hidingpower are observed. This uniform distribution is achieved through theinteraction of the surface modified/treated of the TiO₂ (as supplied bythe TiO₂ manufacturer) and nano particles. The TiO₂ used in the painthas metal oxide surface treatment along with oligomeric/polymericdispersant; which keeps the TiO₂ particles from flocculating to acertain extent in the dry film. Addition of surface treated nanoparticles (treated in house with an oligomeric/polymeric dispersant)further enhances the spacing of TiO₂. Typically, addition of untreatednano particles (ex. ZnO) to a paint would flocculate the TiO₂ and makethe paint useless. However, with the proper pretreatment of both TiO₂and nano particles, electro-steric interactions prevent flocculationfrom occurring in the wet paint and during the paint drying process. Bypreventing the particles from flocculating, optimal TiO₂ spacing isachieved. Although prior art has shown some TiO₂ spacing with extenderpigments, none has been known to produce as effective results.

The ideal spacing of TiO₂ is illustrated in FIG. 1. The TiO₂ particlesare spaced as efficiently as can be, allowing for maximum scattering oflight, and thus, providing the maximum hiding power. FIG. 2 illustrateswhat is believed to occur in current coating formulations. The particlesare not spaced evenly (some are agglomerated); and therefore lightscattering is not optimum and hiding power suffers. FIG. 3 illustratesone possible spacing arrangement in accordance with the principles of apreferred form of the present invention. It is believed that thenanoparticle-sized extender pigment particles, for example illustratedas ZnO, have an affinity for the surface of TiO₂ particles that aides inspacing the TiO₂ particles. Thus, the nanoparticles and TiO₂ interact bya mechanism resulting in improved spacing of the TiO₂ particles.Although both pigmentary and nano ZnO show improvements in tint strength(up to 30%); the nano ZnO particle effect is more efficient. Nano ZnOparticles are also more efficient at improving hide. Although not ideal,the spacing in FIG. 3 has TiO₂ particles which are still spaced betterthan in typical prior art paint systems; thus, the paint provides muchimproved hiding power. It must be appreciated that FIG. 3 isnon-limiting, and that a multitude of various spacing arrangements andmorphologies, providing improved spacing and resulting improved hidingpower, are within the full scope of the present invention.

The positive attributes of nano ZnO particles in paints is resin systemdependent, especially for tint strength and gloss observations. Thus,various resin systems can be used as known in the art. The most profoundand preferred results are seen with acrylic resin systems (bothself-crosslinking and non self-crosslinking). Contrast ratio increasesare observed for all types of resin systems.

Similarly, various pigmentary TiO₂ particles respond differently to theaddition of nano ZnO particles. Thus, various pigmentary TiO₂ particlescan be used in accordance with the principles of the present invention.Commercial sample 1, a TiO₂ product sold under the trade name Kronos4311 by KRONOS Worldwide, Inc., located at 16825 Northcase Drive, Suite1200, Houston, Tex. 77210-4272, responds well in terms of tint strengthand contrast ratio and is a preferred component. Commercial sample 3,sold under the trade name Tiona RCS-2 by Millennium Chemicals, Inc.,located at 20 Wright Avenue, Suite 100, Hunt Valley, Md. 21030, performssimilarly, but it is not as efficient. Commercial sample 2, sold underthe trade name Tiona 596S, also by Millennium Chemicals, Inc., locatedat 20 Wright Avenue, Suite 100, Hunt Valley, Md. 21030, has only minimalimprovements when compared to Commercial sample 1 and Commercial sample3.

-   -   Various dispersants may be used as known in the art.    -   Additional TiO₂ particle content in systems in accordance with        the principles of the present invention increases the tint        strength (up to 40%); however, this improvement is not        significant over paints without additional TiO₂ particles. Hide        is significantly improved with increasing TiO₂ particle content.        Thus, in one embodiment of the present invention, additional        TiO₂ particle content is used as compared to conventional        formulations.

EXAMPLES

A master batch of paint prepared in accordance with the principles ofthe present invention was made holding a portion of water. The batch wasthen apportioned, and the proper amounts of nanoparticles (see examplesbelow) and water were post-added. Various components of the paint werevaried depending on the focus of the experiment. Tint strength andcontrast ratio of each sample were evaluated. Tables 1A-G list the basicformulation for Paints A-G, respectively.

Table 1.

TABLE 1A Paint A (High Gloss: Self-Crosslinking 100% Acrylic) A paintcoating composition comprising of the following raw materials: GenericDescription wt % Range Self-Crosslinking Acrylic Polymer 48-52 TiO2Slurry 31-35 Water 4-8 Ethylene Glycol 2-6 Associative High ShearRheology Modifier 2-6 Alkyl Ester Coalescing Agent 1.5-3.5 HydrophobicCopolymer Dispersant 0.5-2.0 Phosphated Co-ester Surfactant 0.1-0.4Mildewcide 0.1-0.4 Silicone Defoamer 0.1-0.3 Amino Alcohol Additive0.1-0.3 Non-ionic HEUR Low Shear Rheology Modifier 0.1-0.3 SiliconeDefoamer 0.1-0.3 In-can Biocide 0.05-0.1  Silicone based Anti-marAdditive 0.05-0.1 

TABLE 1B Paint B (Semi-Gloss: 100% Acrylic - Low PVC) A paint coatingcomposition comprising of the following raw materials: GenericDescription wt % Range Acrylic Polymer 37-41 TiO2 Slurry 27-31 Water13-17 Opaque Polymer 4-8 Associative High Shear Rheology Modifier 2-6Ethylene Glycol 1.5-4.5 Non-ionic HEUR Low Shear Rheology Modifier0.5-2.5 Texanol 0.5-1.5 Hydrophobic Copolymer Dispersant 0.5-1.5Feldspar (Nepheline Syenite) 0.2-0.8 Butyl Carbitol 0.2-0.8 Non-ionicSurfactant 0.2-0.8 Mildewcide 0.2-0.8 Attapulgite Clay 0.1-0.6 SiliconeDefoamer 0.1-0.4 Mineral Oil Defoamer 0.1-0.4 In-can Biocide 0.05-0.2 

TABLE 1C Paint C (High Gloss - Styrene Acrylic) A paint coatingcomposition comprising of the following raw materials: GenericDescription wt % Range Styrene-Acrylic Polymer 53-57 TiO2 Slurry 30-34Butyl Carbitol 2-6 Ethylene Glycol 2-6 Associative High Shear RheologyModifier 1-4 Texanol 1-4 Water 1-4 Non-ionic Phosphate Ester Surfactant0.2-0.6 Amino Alcohol Additive 0.2-0.6 Mildewcide 0.1-0.5 SiliconeDefoamer 0.1-0.5 Hydrophobic Copolymer Dispersant 0.1-0.5 In-can Biocide0.05-0.15 Non-ionic HEUR Low Shear Rheology Modifier 0.05-0.15 Siliconebased Anti-mar Additive 0.05-0.15

TABLE 1D Paint D (Flat - PVA) A paint coating composition comprising ofthe following raw materials: Generic Description wt % Range TiO2 Slurry24-28 Poly-vinyl Acrylic Emulsion 24-28 Water 14-18 Calcined Kaolin 8-12 Opaque Polymer  7-11 Calcium Carbonate 3-6 Ethylene Glycol 1-4Calcined Diatomaceous Earth 1-4 Non-ionic HEUR Low Shear RheologyModifier 0.5-1.5 Associative High Shear Rheology Modifier 0.5-1.5Mildewcide 0.2-0.6 Non-ionic Surfactant 0.2-0.6 Mineral Oil defoamer0.2-0.6 Hydrophobic Copolymer Dispersant 0.2-0.6 Modified HEC (ModifiedHydroxyethylcellulose) 0.2-0.6 Attapulgite Clay 0.2-0.6 Amino AlcoholAdditive 0.2-0.6 In-can Biocide 0.05-0.25

TABLE 1E Paint E (Semi-gloss: VAE) A paint coating compositioncomprising of the following raw materials: Generic Description wt %Range Vinyl Acetate-Ethylene Emulsion 38-42 TiO2 Slurry 34-38 Water 9-13 30 HEC 5-9 Propylene Glycol 1-4 Texanol 0.5-1.5 HydrophobicCopolymer Dispersant 0.5-1.5 Mildewcide 0.5-1.5 Mineral Oil Defoamer0.2-0.8 Amino Alcohol Additive 0.1-0.4 Phosphasted Co-ester Surfactant0.1-0.4 In-can Biocide 0.05-0.2 

TABLE 1F Paint F (Satin: 100% Acrylic - Mid PVC) A paint coatingcomposition comprising of the following raw materials: GenericDescription wt % Range Acrylic Polymer 35-39 TiO2 Slurry 27-31 Water11-15 Feldspar (Nepheline Syenite) 4-8 Opaque Polymer 4-8 AssociativeHigh Shear Rheology Modifier 2-4 Ethylene Glycol 2-4 Texanol 0.5-2  Non-ionic HEUR Low Shear Rheology Modifier 0.5-2   Mineral Oil Defoamer0.3-1   Attapulgite Clay 0.3-1   Butyl Carbitol 0.3-1   Non-ionicSurfactant 0.3-1   Hydrophobic Copolymer Dispersant 0.2-0.8 Mildewcide0.2-0.8 In-can Biocide 0.05-0.2 

TABLE 1G Paint G (Flat: 100% Acrylic - High PVC) A paint coatingcomposition comprising of the following raw materials: GenericDescription wt % Range Acrylic Polymer 28-32 TiO2 Slurry 22-26 Water11-15 Calcined Kaolin  9-13 Feldspar (Nepheline Syenite)  7-10 OpaquePolymer 1.5-4   Calcium Carbonate 1.5-4   Associative High ShearRheology Modifier 1-3 Ethylene Glycol 1-3 Texanol 0.5-2   HydrophobicCopolymer Dispersant 0.5-2   Non-ionic HEUR Low Shear Rheology Modifier0.25-1   Mineral Oil Defoamer 0.25-1   Non-ionic Surfactant 0.2-0.8Mildewcide 0.2-0.8 Attapulgite Clay 0.1-0.6 Amino Alcohol Additive0.1-0.6 In-can Biocide 0.05-0.2 

Example 1 Nanoparticle Screening

The following nanoparticles were screened in a typical paintformulation: Al₂O₃, SiO₂, and ZnO (two particle sizes) at twoconcentration levels, 0.50% and 1.00%. Particle sizes of thesenanopigments ranged from ˜10-120 nm. TABLE 2 shows the data for thenanoparticle screening tests. The starting Paint A is any conventionalwhite base paint with a PVC of ˜23.0. The concentration of nanoparticlesis a percentage based on the total formula weight.

Three observations are noted from TABLE 2 first, all of the differentnanoparticles studied yield an increase in tint strength and contrastratio when formulated into Paint A (as opposed to Paint A withoutnanopigmentation). Second, improved tint strength and contrast ratio areobserved with various particles sizes (˜10-120 nm). Lastly, increasingthe concentration of nanoparticles (0.5% vs. 1.0%) yields an increase intint strength and contrast ratio. From this screening study, Paint Awith added nano ZnO (˜60 nm particle size) at a concentration of 0.5%yielded the highest increase in tint strength (28.75%) and contrastratio (0.75%). One skilled the art would appreciate that while thecontrast ratio increase is small, a mere increase of 0.40% will show anoticeable visual improvement in hiding power.

TABLE 2 Tint Contrast Nanoparticle Nanoparticle Strength Ratio SampleType Size [Nanoparticle]* Increase Increase Paint A Al₂O₃ ~10 nm 0.5%2.40% 0.70% 1.0% 6.80% 0.40% Paint A SiO₂ ~20 nm 0.5% 5.70% 0.65% 1.0%14.50% 0.50% Paint A ZnO ~60 nm 0.5% 28.75% 0.75% 1.0% 22.70% 0.45%Paint A ZnO ~120 nm  0.5% 20.70% 0.35% 1.0% 27.10% 0.30% *Based on totalformula weight.

Example 2 Nanoparticle Concentration Screening

In this study, the concentration range of nano ZnO (˜60 nm particlesize) was examined in Paint A. The concentrations of nano ZnO examinedwere 0.05%, 0.10%, 0.25%, 0.50%, 1.00%, 1.50%, 2.50%, and 5.00%. TABLE 3shows the tint strength and contrast ratio data for increasing the nanoZnO concentration in Paint A. The concentration of nano ZnO is expressedas a percentage based on total formula weight.

The data in TABLE 3 illustrate that as the concentration of nano ZnO(particle size of ˜60 nm) is increased in the base Paint A (0.05-5.00%),the tint strength and contrast ratio increase (as opposed to Paint Awithout nanopigmentation). The optimum use level of nano ZnO (particlesize ˜60 nm) is 0.50%, yielding a tint strength increase of 28.75% and acontrast ratio of 0.75%.

TABLE 3 Tint Contrast Nanoparticle Nanoparticle Strength Ratio SampleType Size [Nanoparticle]* Increase Increase Paint A ZnO ~60 nm 0.05%1.50% 0.35% 0.10% 3.00% 0.30% 0.25% 14.10% 0.35% 0.50% 28.76% 0.75%1.00% 22.70% 0.45% 1.50% 23.00% 0.40% 2.50% 20.70% 0.35% 5.00% 16.25%0.20% *Based on total formula weight.

Example 3 Blending of Nanoparticles Study

This study examines the effect of blending nanoparticles of differentcomposition and different particle sizes into a typical base paintformulation (Paint B in this case). The nanoparticles studied were ZnO(˜60 nm and ˜120 nm particle size) and Al₂O₃ (˜50 nm particle size).TABLE 4 lists the contrast ratio results for Paint B with various addedblends of nanopigmentation. The nanoparticles are examined alone, andthen as the blends listed in TABLE 4. The concentration for each of thedifferent nanoparticles was 0.50% based on total formula weight. Thebase Paint B is a conventional, well known paint with a PVC of ˜28.0.

TABLE 4 illustrates that when the nanoparticles are used alone or inblends of equal ratios in base Paint B, contrast ratio is increased(opposed to Paint B without nanopigmentation). This increase in contrastratio is noted in all of the listed cases, whether the nanopigments areof approximately equal size (nano ZnO, ˜60 nm blended with nano Al₂O₃,˜50 nm) or are of different sizes (either nano ZnO, ˜60 nm blended withnano ZnO, ˜120 nm or nano Al₂O₃, ˜50 nm blended with nano ZnO, ˜120 nm).In this study, the largest improvement in contrast ratio was observed,0.55%, with the combination of the base Paint B with a blend of nano ZnO(˜120 nm) and nano Al₂O₃ (˜50 nm).

TABLE 4 Contrast Nanoparticle Nanoparticle Ratio Sample Type Size[Nanoparticle]* Increase Paint B ZnO ~60 nm 0.50% 0.20% Paint B ZnO ~120nm  0.50% 0.45% Paint B Al₂O₃ ~50 nm 0.50% 0.40% Paint B-Blend ZnO ~60nm 0.50% 0.35% ZnO ~120 nm  0.50% Paint B-Blend ZnO ~60 nm 0.50% 0.20%Al₂O₃ ~50 nm 0.50% Paint B-Blend ZnO ~120 nm  0.50% 0.55% Al₂O₃ ~50 nm0.50% *Based on total formula weight.

Example 4 Resin Type Screening with Nanoparticles

The following example demonstrates that the most common resin systemstypically used in architectural coatings can be used with thenanotechnology described in this patent. The resin systems that wereexamined in this study were two acrylic resins (one self-crosslinking,one non self-crosslinking), a styrene-acrylic resin, a polyvinyl acrylic(PVA), and a vinyl acetate ethylene (VAE) resin. These commerciallyavailable resins were used to make up several conventional base paintsas set forth in Table 1, Paint A (23.0 PVC), Paint B (28.0 PVC), Paint C(23.0 PVC), Paint D (51.75 PVC), and Paint E (27.64 PVC). All of thesepaints were examined with and without 0.50% (based on total formulaweight) of nano ZnO (˜60 nm particle size). TABLE 5 lists the tintstrength and contrast ratio results for Paints A-E.

The data in TABLE 5 illustrates that the effect of spacing withnanoparticles (ZnO ˜60 nm in this case) is observed in paints made withdifferent resin compositions. All of the various resin types, acrylic(self-crosslinking), acrylic (non self-crosslinking), styrene-acrylic,PVA, and VAE in Paints A-E all show an improvement in tint strength andcontrast ratio (over Paints A-E without nanopigmentation). The mostdramatic improvement in tint strength and contrast ratio is observedwith additions to base Paint A, which was formulated with a 100%self-crosslinking acrylic resin. Paint A, as modified, shows a 28.75%increase in tint strength and a 0.75% increase in contrast ratio.

TABLE 5 Tint Contrast Nanoparticle Nanoparticle Strength Ratio SampleResin Type Type Size [Nanoparticle]* Increase Increase Paint A AcrylicZnO ~60 nm 0.50% 28.75% 0.75% (Self x- linking) Paint B Acrylic ZnO ~60nm 0.50% 13.20% 0.80% (Non x- linking) Paint C Styrene- ZnO ~60 nm 0.50%7.10% 0.30% Acrylic Paint D PVA ZnO ~60 nm 0.50% 3.30% 0.20% Paint E VAEZnO ~60 nm 0.50% 3.80% 0.10% *Based on total formula weight.

Example 5 Pigmentary TiO₂ Screening with Nanoparticles

This study examines several different commercially available pigmentaryTiO₂ types and their ability to be spaced with nanoparticles (ZnO, ˜60nm particle size in this case) as described in this patent. Threedifferent pigmentary TiO₂ products were studied as additives in basePaint A, with and without nanopigmentation (0.50% ZnO, based on totalformula weight). The three different TiO₂ products studied wereCommercial-1, Commercial-2, and Commercial-3 previously described. TABLE6 lists tint strength and contrast ratio data for these Paints.

The data in TABLE 6 illustrates that an improvement in tint strength andcontrast ratio is observed in base Paint A, as modified, with all threecommercially available pigmentary TiO₂ types. The largest improvement isnoted in modified Paint A with TiO₂ type Commercial-1, showing anincrease in tint strength of 28.75% and contrast ratio increase of0.75%.

TABLE 6 Tint Contrast Nanoparticle Nanoparticle Strength Ratio SampleTiO₂ Type Size [Nanoparticle]* Increase Increase Paint A Commercial 1ZnO ~60 nm 0.50% 27.80% 0.75% Paint A Commercial 2 ZnO ~60 nm 0.50%14.50% 0.55% Paint A Commercial 3 ZnO ~60 nm 0.50% 20.10% 0.65% *Basedon total formula weight.

Example 6 Pigmentary TiO₂ Concentration Screening with Nanoparticles

This example demonstrates that nanoparticles (ZnO, ˜60 nm in this case)can be used to effectively space various levels of pigmentary TiO₂ in atypical architectural coatings formulation. Paint A was studied withvarious added levels of Commercial-1 TiO_(2; 7.10)%, 10.70%, 14.20%,17.80%, 21.10%, 24.90%, and 28.50% (based on total formula weight) withand without nanopigmentation (0.50% of nano ZnO, ˜60 nm). TABLE 6 liststhe tint strength and contrast ratio data for these paints.

TABLE 7 illustrates that at every level of pigmentary TiO₂ examined, animprovement in tint strength and contrast ratio is observed (as comparedto the corresponding paint without nanopigmentation). The largestincrease in tint strength and contrast ratio is observed with modifiedPaint A having 24.90% TiO₂ (based on total formula weight) with 0.50%˜60nm nano ZnO (based on total formula weight); this paint shows a 29.25%increase in tint strength and a 0.90% increase in contrast ratio.

TABLE 7 Tint Contrast [TiO₂]* Nanoparticle Nanoparticle Strength RatioSample (Commercial-1) Type Size [Nanoparticle]* Increase Increase PaintA 7.10% ZnO ~60 nm 0.50% 10.00% 0.60% Paint A 10.70% ZnO ~60 nm 0.50%12.75% 0.60% Paint A 14.20% ZnO ~60 nm 0.50% 19.75% 0.55% Paint A 17.80%ZnO ~60 nm 0.50% 23.00% 0.65% Paint A 21.10% ZnO ~60 nm 0.50% 27.25%0.35% Paint A 24.90% ZnO ~60 nm 0.50% 29.25% 0.90% Paint A 28.50% ZnO~60 nm 0.50% 25.25% 0.40% *Based on total formula weight.

Example 7 PVC Variation with Nanopigmentation

This example demonstrates that nanoparticles (ZnO, ˜60 nm in this case)can be used to effectively space pigmentary TiO₂ in typicalarchitectural paints of varying PVC. Paints of three different PVC'swere examined in this study (all with the same resin and TiO₂ types) atPVC's ranging from ˜28.0-50.50 PVC. TABLE 8 lists the tint strength andcontrast ratio improvements for these three paints.

TABLE 8 illustrates that for the PVC range of ˜28.0-50.50 PVC, animprovement in tint strength and contrast ratio is noted. The bestimprovement in this particular study was with modified Paint B (28.10PVC) with tint strength improved by 5.50% and contrast ratio improved by0.40%.

TABLE 8 Nanoparticle Nanoparticle Tint Strength Contrast Sample PVC TypeSize [Nanoparticle]* Increase Ratio Increase Paint B 28.10 ZnO ~60 nm0.50% 5.50% 0.40% Paint F 34.90 ZnO ~60 nm 0.50% 2.40% 0.45% Paint G50.40 ZnO ~60 nm 0.50% 2.40% 0.50% *Based on total formula weight.

1. A process for preparing a coating composition, comprising: dispersinga plurality of titanium dioxide particles, pretreated with a metaloxide, with a dispersant in a first dispersion medium; mixing ananoparticle metal oxide pigment, pre-treated to minimize flocculation,and the first dispersion medium containing the titanium dioxideparticles; and interacting the nanoparticle pigment and the titaniumdioxide particles to form an intervening dispersion of a plurality ofnanoparticle pigment substantially uniformly distributed around thetitanium dioxide particles.
 2. The process of claim 1, wherein thenanoparticle mixed oxide pigment comprises zinc oxide.
 3. The process ofclaim 1, wherein the step of dispersing the titanium dioxide particlesin a first dispersion medium comprises using the dispersant which isselected from the group consisting of ammonia salt hydrophobic copolymerdispersant and high molecular weight block copolymer.
 4. The process ofclaim 1, wherein the step of mixing a nanoparticle metal oxide pigmentcomprises mixing a first nanoparticle metal oxide pigment having a firstaverage particle size and a second nanoparticle metal oxide pigmenthaving a second average particle size, the first nanoparticle metaloxide pigment and the second nanoparticle metal oxide pigment havingpre-treated surfaces to minimize flocculation.
 5. The process of claim4, wherein the first average particle size is about 120 nm and thesecond average particle size is about 60 nm.
 6. The process of claim 4,wherein the first average particle size is about 120 nm and the secondaverage particle size is about 50 nm.
 7. The process of claim 5, whereinmixing the nanoparticle metal oxide pigment comprises a 0.05% to 5.00%by weight of the nanoparticle metal oxide pigment.
 8. The process ofclaim 5, wherein the titanium dioxide particles comprises between about7.1 and about 28.5 percent by weight of the coating composition.
 9. Theprocess of claim 5, wherein the PVC of the coating composition isbetween about 28.0 and 50.50.